What is Protein? - Definition, Function, Benefits & Sources

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  • 0:02 Protein: The Inside Story
  • 0:48 Amino Acids & Proteins
  • 1:25 Sources of Protein
  • 2:37 Lesson Summary
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Lesson Transcript
Dominic Corsini
Expert Contributor
Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

In this lesson, you'll learn about the primary structure, function, and sources of protein molecules while exploring some real-world examples and illustrations.

Protein: The Inside Story

The human body uses proteins for many things, including repairing and building tissues, acting as enzymes, aiding the immune system, and serving as hormones. Each of these important functions requires a slightly different form of protein. In spite of their differences in structure, all proteins contain the same basic sub-components.

Proteins are one of the four different types of macromolecules, in addition to carbohydrates, lipids, or fats, and nucleic acids, such as DNA and RNA. Macromolecules are large molecules that perform specialized functions inside living organisms. The structural arrangement of a protein molecule will differ in accordance with its function.

Amino Acids & Proteins

Proteins are long chains of amino acids. Amino acids are the building blocks of protein. In other words, amino acids are like the links in a chain. The chain itself represents the protein molecule. Protein chains are then twisted and folded together in specific ways to create certain molecules.

This example shows our primary protein chain as it's twisted into a helical shape, folded into a sheet, and then twisted all over again into an intricate globular shape. In this case, the final product is a protein molecule known as hemoglobin, which can be found in your blood.

Sources of Protein

Earlier, we mentioned that protein plays a role in tissue repair, and that's why it's so important to have protein in your diet. But what are the best sources of protein? And, are there different types of protein? Let's explore these questions. Afterwards, you might take a look in your refrigerator and decide whether your diet is protein rich or protein poor.

Protein can be found in all living things. The type and amount of protein within foods can vary, but inevitably, it's there in some form. Meats, cheeses, and nuts tend to have a higher protein content than many plant-based sources. To determine the protein content of a food, we'll need to read its nutrition label.

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Additional Activities

Protein Word Search Activity

This activity will help you assess your knowledge of the function, benefits, and sources of protein.


For this activity, print this page on a blank piece of paper. Search and highlight the word that will complete each of the given clues. Afterward, write them on the appropriate blank space in the clues.


  1. A _____ is a very large molecule, especially used in reference to large biological polymers such as nucleic acids and proteins.
  2. One of the primary roles of protein is to act as _____ and increase the rate of chemical reaction in the body.
  3. Red meat, poultry, and fish are some examples of _____ proteins.
  4. Hemoglobin is a type of protein molecule that has a distinct _____ shape.
  5. Proteins can act as chemical-signaling molecules known as _____ to control or regulate physiological processes.
  6. _____ are any of a group of organic compounds including the fats that are classified as macromolecules.
  7. Eating peas, beans, and grain will not provide all of the amino acids your body needs since these are _____ proteins.
  8. The building blocks of proteins are known as _____ acids.
  9. The _____ of a protein molecule will vary depending on its function.
  10. _____ repair is aided by proteins that speed up wound healing through the synthesis of new satellite cells.

Answer Key

  8. AMINO
  10. TISSUE

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